Machines for compression molding closure shells typically include a turret or carousel that rotates around a vertical axis. A plurality of molds around the periphery of the carousel include male and female mold sections that are aligned along vertical axes parallel to the axis of rotation. Cams drive one or both of the mold sections of each pair between an open spaced-apart position, in which a molded closure shell is stripped from the male mold section and a charge of plastic material is placed in the female mold section, and a closed position in which the male and female mold sections are brought together to compression mold the charge to form the closure shell. U.S. Patents that illustrate machines of this type for compression molding plastic closure shells include U.S. Pat. Nos. 5,670,100, 5,989,007, 6,074,583 and 6,478,568.
When compression molding closure shells in machines of this type, the shell typically is stripped from the male mold core by means of a sleeve that engages the edge of the closure skirt. The sleeve and/or the core are moved axially relative to each other so that the closure skirt effectively is pushed off of the core. This type of stripping action is satisfactory for many applications, but is not satisfactory for applications that require precise control and/or contouring of the internal thread segments on the closure shell, such as retort applications in which the closure must remain on the container finish under high temperature and pressure conditions. In applications of this type, the closure must be stripped from the core by rotating the closure off of the core. U.S. Pat. No. 6,706,231 discloses a vertical-axis carousel-type machine for compression molding closure shells, in which a cam-operated ball screw arrangement rotates the mold core to unthread the mold core from the closure shell and strip the shell from the core.
The present disclosure involves a number of aspects or inventions, which may be implemented separately from or in combination with each other.
A machine for compression molding plastic closures in accordance with one aspect of the present disclosure includes a support mounted for rotation around an axis, and a plurality of compression molds on the support at angularly spaced positions around the axis. Each of the molds includes a male mold section and a female mold section, at least one of which is movable with respect to the other between a closed position to form a compression mold cavity and an open position spaced from each other. The male mold section includes a mold core and a stripper sleeve surrounding the mold core for movement both rotationally and axially of the mold core. A first screw drive couples the female mold section to the stripper sleeve for rotating the stripper sleeve around the mold core as the at least one mold section is moved between the closed and open positions. A second screw drive couples the stripper sleeve to the support to move the stripper sleeve axially over the mold core as the stripper sleeve is rotated around the core. The stripper sleeve thus rotationally and axially removes a closure shell molded around the core as the at least one mold section is moved with respect to the other from the closed toward the open position. The support may comprise a horizontal wheel as in a carousel-type compression molding machine or a vertical wheel that is rotatable around a horizontal axis. The at least one mold section may be cam driven between the open and closed positions as a function of rotation of the support around its axis.